Inspection method and apparatus for detecting oversized apertures in relatively thin sheets of opaque material

ABSTRACT

An inspection method and apparatus for detecting oversized apertures in thin sheets of opaque material utilizing a light source positioned in an encasement means having a floor and a plurality of upstanding walls about the perimeter of the floor. Each of these walls has a ledge formed thereon for supporting a translucent enclosure member having a predetermined pattern of openings spaced therein. As a relatively thin sheet of apertured material is positioned on the surface of the enclosure member according to alignment pins on the surface, a comparator means, hingedly affixed to one side of the enclosure member and comprising a relatively thin sheet of transparent material having an opaque pattern formed thereon corresponding to the aperture pattern desired for the opaque material, is lowered to cover the opaque material. Oversized apertures are detected if light is emitted through the adjoining comparator means and opaque material.

United States Patent 1 Tulk et al.

[in 3,711,205 1 Jan. 16,1973

[54] INSPECTION METHOD AND APPARATUS FOR DETECTING OVERSIZED APERTURES IN RELATIVELY THIN SHEETS OF OPAQUE MATERIAL [75] invemar z'xiamaer swan Tulk, Alan David Douglas, Ivan L. Ericson, all of Towanda, Pa. 18848 [73] Assignee: GJE Sylvania Inc.

[22] Filed: July 22, 1971 21 Appl. No.: 165,193

[52] U.S. Cl. ..356/162, 250/219 DF, 356/168, 356/204, 356/237 [51] Int. Cl. ..G0lb ll/OO [58] Field of Search ..356/l56, 162, 165, 168, 237, 356/204; 250/219 DF [56] References Cited UNITED STATES PATENTS 1,135,919 4/1915 Pilkington ..356/l68 3,614,232 10/1971 Mathisen..... 3,617,744 11/1971 Irish 3,514,208 5/1970 Levin 2,689,779 9/1954 Grimm et al. ..316/29 3,299,273 l/l967 Sturdevant ..356/l68 Primary Examiner-Ronald L. Wibert Assistant Examiner-J. Rothenberg Att0rneyNorman J. OMalley et al.

[57] v ABSTRACT An inspection method and apparatus for detecting Oversized apertures in thin sheets of opaque material utilizing a light source positioned in an encasement means having a floor and a plurality of upstanding walls about the perimeter of the floor. Each of these walls has a ledge formed thereon for supporting a translucent enclosure member having a predetermined pattern of openings spaced therein. As a relatively thin sheet of apertured material is positioned on the surface of the enclosure member according to alignment pins on the surface, a comparator means, hingedly affixed to one side of the enclosure member and comprising a relatively thin sheet of transparent material having an opaque pattern formed thereon corresponding to the aperture pattern desired for the opaque material, is lowered to cover the opaque material. Oversized apertures are detected if light is emitted through the adjoining comparator means and opaque material.

10 Claims, 4 Drawing Figures PATENTEUJAH 16 ms 3. 71 1-, 205

SHEET 1 0r 2 INVENTORS ALEXANDER S. TULK.

ALAN D. DOUGLAS. &

lVAN L. ERICSON BY 33m ATTORNEY PATENTED JAN 16 I975 SHEET 2 OF 2 INVENTORS ALEXANDER S. TULK.

ALAN D. DOUGLAS. &

IVAN L. ERICSON ATTORNEY INSPECTION METHOD AND APPARATUS FOR DETECTING OVERSIZED APERTURES IN RELATIVELY THIN SHEETS OF OPAQUE MATERIAL BACKGROUND OF THE INVENTION This invention relates to inspection apparatus and more particularly to an apparatus for inspecting for oversized apertures in relatively thin sheets of opaque material.

One typical example of opaque material having apertures located therein is the conventional aperture or shadow mask found in most color television cathode ray tubes. The purpose of this mask is to insure that electron beams emitted from electron guns positioned in the neck of the tube strike the proper phosphor dots found in the cathodoluminescent screen formed on the viewing portion of the tube.

These masks are produced from sheets of very thin metal, usually low carbon steel, and contain thousands of very small apertures, or holes. These holes are usually etched from the metal through the employment of photographic and etching techniques standard in the industry. After photoprinting a hole pattern on the masks surfaces, etching solutions are sprayed on to remove the exposed areas. After etching, the masks are cut and formed to coincide with the internal portion of the cathode ray tube screen. I

It can be readily seen therefore, that in order to attain correct alignment between the electron beams and corresponding phosphor dots on the screen, it is exceedingly important that the apertures in the mask are maintained within close tolerances and are not over sized.

One previous method ofinspecting shadow masks for such flaws involved an operator placing each mask on a table having a transparent top and light source positioned beneath. A careful and tedious study of the mask was then undertaken utilizing some form of magnification means. In addition to being excessivelytime consuming, this and similar methods produced a relatively high fatigue factor which consequently resulted in a substantial reduction in accuracy.

OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a new and unique apparatus for inspecting for oversized apertures in sheets of thin opaque material.

It is another object of this invention to provide a new method for inspecting for oversize apertures in sheets of thin opaque material.

It is a further object of this invention to provide an apparatus for inspecting for oversized apertures in cathode ray tube shadow masks which substantially reduces the aforementioned disadvandages of prior art methods.

In accordance with one aspect of the invention, there is shown an encasement means having a light source positioned therein. The encasement means comprises a boxlike structure having a floor and a plurality of upstanding walls positioned about the perimeter of the floor. Each of the upstanding walls is provided with a terminal means for seating a translucent enclosure member to which is hingedly affixed a comparator means.

To inspect a thin sheet of apertured opaque material, an operator places the material on the translucent enclosure member and aligns itaccording to alignment means positioned on the enclosure member. The operator then lowers the comparator means to substantially cover the material. To provide a snug fit between the comparator means and the material to be inspected, a vacuum is created within the encasement means by a vapor extraction means positioned externally of the encasement means. As vapor is withdrawn through an established opening in the floor of the encasement means, a suction force is created between the material and comparator means by the vapor as it is withdrawn through the apertures within the material and designated openings within the enclosure member. As the material and comparator means are drawn together, an opaque pattern on the comparator means which is representative of the aperture pattern desired for the opaque material aligns with the apertures to be inspected. In the event that one or more apertures are oversized, light will pass through the adjoining comparator means and material and can easily be detected by the operator. Should this occur, the material is rejected and eliminated for further production purposes.

In accordance with another aspect of the invention, there is described a method for detecting oversized apertures in thin sheets of opaque material having these apertures positioned therein according to a predetermined pattern. This method comprises aligning the predetermined pattern of apertures of one sheet of opaque material with a pre-established pattern of opaque dots formed on a sheet of transparent material, this pre-established pattern of dots being desired for the pattern of apertures. A light source is then provided on one side of the aligned patterns and the other side is inspected for any light transmitted through the patterns, the light thereby indicating oversized apertures.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of one embodiment of the present invention and one type of apertured opaque material which it can inspect, a cathode ray tube shadow mask.

FIG. 2 is an elevational view, in section, showing the shadow mask positioned on the present invention as it is to be inspected.

FIG. 3 is a plan view showing one example of an oversized aperture which may be detected by the present invention.

FIG. 4 is a sectional view as taken along the line 4-4 in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings.

With reference to the drawings, one embodiment of the present invention, apparatus 11 is shown in FIG. l. Encasement means 13 comprises a floor l5 surrounded on its perimeter by a plurality of upstanding walls 17 and is shown to house a plurality of electric lights 19. Near the upper portions of each upstanding wall 17 terminal means 21 are formed in order that translucent enclosure member 23 may be seated thereon. Each of said terminal means 21 in this particular embodiment comprises a ledge, this ledge substantially parallel to the upper edge 24 of each upstanding wall 17 and extending substantially the entire length of the internal portions 25 of the walls.

An additional possibility for terminal means 2l could comprise a plurality of pins 22 partially inserted into the internal portions 25 of walls 17 at a predetermined distance from upper edges 24 of each wall, this embodiment illustrated in FIG. 2.

Enclosure member 23 which may be formed of any translucent material such as clear plastic or glass, has a plurality of spaced openings 26 therein.

Apertured opaque material 27, in this case represented by a cathode ray tube shadow mask, is positioned on translucent enclosure member 23 by aligning upstanding pins 29 on the enclosure member with corresponding indentations 31 in material 27. Once positioned, the material is held against enclosure member 23 by a suction force acting through spaced openings 26 as a result of vapor being withdrawn from encasement means 13 though opening 33 within floor 15. The vapor is withdrawn through hose 35 by a vapor extraction means (not shown) positioned externally of the encasement means. Although several other methods are possible, the vapor extraction means as utilized by the Applicants of this disclosure comprises a motor driven air pump.

To inspect material 27 for oversized apertures, the operator of the apparatus lowers the comparator means 37 to substantially cover the material. Comparator means 37, which is hingedly affixed by tape 38 to one end of enclosure member 23, fits snugly over the material as a result of the previously described suction force, in this case acting through apertures 39 in the material. While the embodiment in FIG. 1 shows comparator means 37 hinged to an end of enclosure member 23, this is by no means a limiting factor concerning operation of the apparatus. Comparator means 37 could be hingedly affixed at any of several other possible locations, such as to one of the internal portions 25 or one of the upper edges 24 of upstanding walls 17.

Comparator means 37 as shown, comprises a photographic transparency developed from an acceptable shadow mask utilizing common photographic techniques, such as drawing the aperturemask and a sheet of negative paper together, exposing the sheet through the mask, and then photochemically removing the non-exposed portions of the negative material from the paper, this paper being of material of transparent nature, such as plastic. This process results in a pliable sheet of transparent material 41, having a plurality of opaque dots 43 formed thereon, these dots in a pattern corresponding to the aperture pattern desired for the shadow mask. When the mask and comparator means are drawn together, as shown in FIG. 2, opaque dots 43 align with corresponding apertures 39 to produce a totally opaque cover as viewed from above by the apparatus operator, provided of course that the mask is an acceptable one.

In FIG. 2 can also be seen hose 35 attached to opening 33 in floor of encasement means 13, through which vapor is continuously being withdrawn (as indicated by illustrated arrows). The vapor is withdrawn through spaced openings 26 and apertures 39 to provide continual suction force between mask and comparator. Once inspection has terminated, the operator lifts both mask and comparator from enclosure means 23. The suction force acting against the mask and comparator, while sufficient to provide a relatively strong bond between the members, is not sufficient to restr ct the movements of the operator during this removal. To substantially eliminate the possibility of injury to the operators hands as a result of encountering the relatively sharp edges of both the mask and comparator means, slot 45 (shown in FIG. 1) is cut from enclosure member 23 in order that the operator may lift both mask and comparator from beneath, rather than having to slide them and possibly incur such an injury.

To avoid interference between comparator means 37 and upstanding pins 29 when the comparator is lowered for inspection, grooves 47 are provided in the non-opaqued area of comparator means 37.

An oversized aperture 49, shown in FIG. 3, is most usually the result of improper etching of the shadow mask. It can be readily understood that this configuration, when compared to desired apertures 39, would permit electron beams to overlap and strike adjacent phosphor dots, thereby causing incorrect color combinations.

FIG. 4, taken along line 4-4 in FIG. 3, is an enlarged elevational view in section showing what occurs when mask 27, having oversized aperture 49 therein, is covered by comparator means 37. Opaque dots 43 align accordingly with the masks apertures as explained in the description of FIG. 2, with the exception that in this case oversized aperture 49, being larger in area than corresponding opaque dots 43, permits light (indicated by dashed lines 51) to pass through. This light indicates to the operator that a flaw in the mask is present and consequently the mask is rejected from further production.

Although there is shown an apparatus which is operated in a manner so as to necessitate individual.

handling of each mask or sheet of similar type material, it can be understood that many movements of the operator could be eliminated through the implementation of various modifications to the apparatus. Should the material to be inspected be in the form of continuous strips, slots could be provided in the upper portion of two opposing upstanding walls at a position above the enclosure member to thereby provide a guide means for the strip. The strip could also be provided with spaced indentations to align with upstanding pins strategically located'on the enclosure member.

Thus, there has been illustrated and described an apparatus and a preferred embodiment of a method. for inspecting apertures in relatively thin sheets of opaque material which allows an operator to rapidly scan the entire sheet of material for oversized apertures in a minimal time period while greatly reducing the possibilities of operator fatigue, injury, and error. Although other apparatus may be used to accomplish the objectives of this invention, the embodiment as shown and described utilizes components believed to be most applicable for aperture mask production.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. An apparatus for inspecting for oversized apertures in relatively thin sheets of opaque apertured material comprising:

an encasement means having a light source located therein, said encasement means comprising a floor having an opening therein and a plurality of upstanding walls around the perimeter of said floor, each of said upstanding walls having a terminal means located thereon for seating a translucent enclosure member, said translucent enclosure member having a plurality of spaced openings established in a predetermined pattern therein and an alignment means located thereon for aligning one of said sheets of opaque apertured material as said sheet is positioned on said translucent enclosure member; and

a comparator means hingedly affixed to said translucent enclosure member and formed to substantially cover said material, said comparator means having an opaque pattern formed thereon, said pattern corresponding to a pattern of apertures desired for said material.

2. The apparatus according to claim 1 in which said comparator means is retained against said material by a suction force created in said encasement means by a vapor extraction means located externally of said encasement means and joined to said opening in said floor of said encasement means, said suction force acting through said spaced openings in said translucent enclosure member and said apertures in said material.

3. The apparatus according to claim 1 in which each of said terminal means comprises a ledge formed along the internal upper portion of each of said upstanding walls and extending substantially the entire length of said internal upper portion of said upstanding wall.

4. The apparatus according to claim 1 in which said terminal means comprises a plurality of pins, a portion of said pins inserted into the internal portions of said upstanding walls at a predetermined distance from the upper edges of said walls.

5. The apparatus according to claim 1 in which said alignment means comprises a plurality of upstanding pins positioned in a pre-established pattern on said translucent enclosure member, said upstanding pins formed to engage corresponding indentations in said material.

6. The apparatus according to claim 1 in which said comparator means comprises a photographic transparency, said transparency having a plurality of opaque dots positioned on a sheet of pliable transparent material according to a pattern acceptable for said apertures in said material.

7. The apparatus according to claim 1 in which said translucent enclosure member has a slot formed therein which is positioned in said enclosure member in a manner so as to be partially covered by said material and said comparator means during inspection of said material, thereby enabling the o erator of said apparatus to lift said materia and sat comparator means from said enclosure member after said inspection is completed.

8. The apparatus according to claim 1 in which said comparator means is hingedly affixed to one of said upstanding walls of said encasement means.

9. An inspection method for detecting oversized apertures in relatively thin sheets of opaque material having said apertures positioned therein according to a predetermined pattern, said method comprising:

mutually aligning said predetermined pattern of apertures within one of said sheets of opaque material with a pre-established pattern of opaque dots on a sheet of transparent material, said pre established pattern of opaque dots being formed in accordance with an acceptable aperture pattern, said aligning being accomplished by utilizing a suction force acting through said apertures in said opaque material and against said sheet of transparent material; providing a light source on one side of said mutually aligned aperture and opaque dot patterns; and

inspecting the opposing side of said mutually aligned aperture and opaque dot patterns for light transmitted through said patterns.

10. The method according to claim 9 which includes the additional step of forming said pre-established pattern of opaque dots on said sheet of transparent material by bringing a sheet of opaque material having a predetermined pattern of desired apertures positioned therein together with a sheet of photographic negative paper, exposing the negative paper through the opaque apertured material and photochemically removing the unexposed portions of negative material from said paper, said paper being of transparent material. 

1. An apparatus for inspecting for oversized apertures in relatively thin sheets of opaque apertured material comprising: an encasement means having a light source located therein, said encasement means comprising a floor having an opening therein and a plurality of upstanding walls around the perimeter of said floor, each of said upstanding walls having a terminal means located thereon for seating a translucent enclosure member, said translucent enclosure member having a plurality of spaced openings established in a predetermined pattern therein and an alignment means located thereon for aligning one of said sheets of opaque apertured material as said sheet is positioned on said translucent enclosure member; and a comparator means hingedly affixed to said translucent enclosure member and formed to substantially cover said material, said comparator means having an opaque pattern formed thereon, said pattern corresponding to a pattern of apertures desired for said material.
 2. The apparatus according to claim 1 in which said comparator means is retained against said material by a suction force created in said encasement means by a vapor extraction means located externally of said encasement means and joined to said opening in said floor of said encasement means, said suction force acting through said spaced openings in said translucent encLosure member and said apertures in said material.
 3. The apparatus according to claim 1 in which each of said terminal means comprises a ledge formed along the internal upper portion of each of said upstanding walls and extending substantially the entire length of said internal upper portion of said upstanding wall.
 4. The apparatus according to claim 1 in which said terminal means comprises a plurality of pins, a portion of said pins inserted into the internal portions of said upstanding walls at a predetermined distance from the upper edges of said walls.
 5. The apparatus according to claim 1 in which said alignment means comprises a plurality of upstanding pins positioned in a pre-established pattern on said translucent enclosure member, said upstanding pins formed to engage corresponding indentations in said material.
 6. The apparatus according to claim 1 in which said comparator means comprises a photographic transparency, said transparency having a plurality of opaque dots positioned on a sheet of pliable transparent material according to a pattern acceptable for said apertures in said material.
 7. The apparatus according to claim 1 in which said translucent enclosure member has a slot formed therein which is positioned in said enclosure member in a manner so as to be partially covered by said material and said comparator means during inspection of said material, thereby enabling the operator of said apparatus to lift said material and said comparator means from said enclosure member after said inspection is completed.
 8. The apparatus according to claim 1 in which said comparator means is hingedly affixed to one of said upstanding walls of said encasement means.
 9. An inspection method for detecting oversized apertures in relatively thin sheets of opaque material having said apertures positioned therein according to a predetermined pattern, said method comprising: mutually aligning said predetermined pattern of apertures within one of said sheets of opaque material with a pre-established pattern of opaque dots on a sheet of transparent material, said pre-established pattern of opaque dots being formed in accordance with an acceptable aperture pattern, said aligning being accomplished by utilizing a suction force acting through said apertures in said opaque material and against said sheet of transparent material; providing a light source on one side of said mutually aligned aperture and opaque dot patterns; and inspecting the opposing side of said mutually aligned aperture and opaque dot patterns for light transmitted through said patterns.
 10. The method according to claim 9 which includes the additional step of forming said pre-established pattern of opaque dots on said sheet of transparent material by bringing a sheet of opaque material having a predetermined pattern of desired apertures positioned therein together with a sheet of photographic negative paper, exposing the negative paper through the opaque apertured material and photochemically removing the unexposed portions of negative material from said paper, said paper being of transparent material. 